In the recent development of semiconductor fabrication technology, the continuous miniaturization in device fabricated demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 .mu.m range, a cleanliness class of 100.about.1000 (which means the number of particles at sizes larger than 0.5 .mu.m per cubic foot) was sufficient. However, when the feature size is reduced to 0.25 .mu.m, a cleanliness class of 0.1 is required. It has been recognized that an inert minienvironment may be the only solution to future fabrication technologies when the device size is reduced further. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness minienvironment that is constantly flush with ultrapure nitrogen that contains no oxygen and moisture.
Different approaches in modem clean room design have been pursued in recent years with the advent of the ULSI technology. One is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16M and 64M DRAM products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered. This stringent requirement creates a new minienvironment concept which is shown in FIG. 1. Within the enclosure of the minienvironment of a process tool 10, an extremely high cleanliness class of 0.1 (which means the number of particles at sizes larger than 0.1 .mu.m per cubic foot) is maintained, in contrast to a cleanliness class of 1000 for the overall production clean room area 12. In order to maintain the high cleanliness class inside the process tool 10, the loading and unloading sections 14 of the process tool must be handled automatically by an input/output device such as a SMIF (standard mechanical interfaces) apparatus. A cassette of wafer can be transported into the process tool 10 by a SMIF pod 18 situated on top of the SMIF apparatus 20.
In a conventional SMIF apparatus 20 such as that shown in FIG. 1, the apparatus 20 consists of a robotic transfer system (not shown) or a robotic arm which is normally configured for gripping the top of a cassette 30 from a platform on which the cassette 30 placed (inside a pod). The robotic arm, sometimes replaced by a gripper assembly, is capable of transporting the cassette 30 into the process tool and place it onto a platform 16 vertically such that the cassette 30 is oriented horizontally. At the beginning of the process, an operator positions a SMIF pod 18 on top of a platform/elevator 22 which contains a cassette 30 holding, for instance, 24 wafers in an upright position. The elevator then descends into the SMIF apparatus 20 for the robotic arm to transport the cassette 30 into the process tool. The SMIF system 20 is therefore capable of automatically utilizing clean isolation technology to maintain a high class clean room effectiveness near wafers and processing equipment. The operation of the robotic arm or the gripper is controlled by an ancillary computer (not shown) or by the process tool 10. The cassette 30 carries wafers or other substrates that are being processed.
The SMIF apparatus 20 has a port (or opening) 24 which is intimately mated with an opening 26 in the sidewall 28 of the process tool 10. The SMIF pod 18 is a sealed container with an opening at the bottom and therefore is capable of preventing contamination to the cassette held therein. The pod may also be equipped by a tagging system for the automated identification and recognition of the parts contained in the pod to prevent mis-processing of the wafers and to track through the host computer of the product-lot serial numbers. The tagging system is mounted on the pod with a probe assembly mounted on the port of the SMIF apparatus 20. The SMIF apparatus 20 is therefore an effective interface between an operator and the process tool 10 in that the transporting of cassette can be conducted in a completely automated fashion to avoid human contact by the operator. This insures that the cassette 30 is transported through a highly clean environment into the process tool 10.
Occasionally, the SMIF apparatus 20 or the process tool 10 requires repair or maintenance procedures to be performed on them. When one of such requirements arises, the SMIF apparatus 20 must be disassembled from the process tool 10 and be physically pushed away in order to provide access to an operator for performing the repair or maintenance.
In a conventional set-up, the SMIF apparatus 20 is attached to the process tool 10 on the side 20 of the tool by a mechanical latch and by a number of bolts attached on the side that is opposite to the latch side. This is shown in FIG. 2. One side of the SMIF apparatus 20 provides a mechanical interlock 32 which is latched into an undercut 34 in the process machine 10. On the opposite side of the SMIF apparatus, bolts 38 are used to attach the apparatus to the process tool.
After a repair or maintenance schedule has been performed on the SMIF apparatus 20 or the process tool 10, the SMIF apparatus is reattached to the process tool by first latching the mechanical interlock 32 and then attaching the bolts 38. However, when the attachment of the mechanical interlock 32 or the bolts 38 is not properly performed such that the SMIF apparatus 20 is not properly attached to the process tool 10, there is no indication or warning signal to tell the operator that the reassembly process is incomplete. Therefore, when the loading of cassette 30 from a SMIF pod 18 is started which causes the movement of the robotic arm, the arm shifts the center of gravity of the SMIF apparatus 20 and thus cause the SMIF to move out of its supposed locked position. Since most SMIF apparatus are installed on wheels, the movement of the SMIF apparatus away from a process tool can easily occur by the shift in gravity caused by the movement of the robotic arm. The mis-position of the SMIF apparatus is not recognized by the host computer and therefore, the robotic arm does not realize when it has delivered the cassette to a position that is not its intended destination. The robotic arm releases the cassette when instruction from the host computer is received and the cassette is left in a unstable position in the process tool. The unstable cassette may tip-over and thus cause severe damage to the wafers when they fall out of the cassette leading to a severe drop in yield.
It is therefore an object of the present invention to provide a method of mounting a wafer loading device to a semiconductor process tool that does not have the drawbacks or shortcomings of a conventional mounting method.
It is another object of the present invention to provide a method of mounting a wafer loading device to a semiconductor process tool that includes the utilization of a warning device to indicate when the loading device is not properly attached to the process tool.
It is a further object of the present invention to provide a method for mounting a wafer loading device to a semiconductor process tool that is capable of providing a signal to a controller for disabling the loading device when a detection that the device is not properly mounted to the process tool is made.
It is another further object of the present invention to provide a method for mounting a wafer loading device to a semiconductor process tool that utilizes spring means in the mounting surface of the loading device such that the device pushes itself away from the process tool when it is not securely attached to the tool.
It is still another object of the present invention to provide a method for mounting a wafer loading device to a semiconductor process tool by using microswitches at the mounting surface of the device such that an improperly mounted device can be readily detected and a signal can be sent out to a controller for disabling the loading device.